Multisite dual surface monophasic action potential mapping in vivo: further evidence of three dimensional characteristics of atrial repolarization

We have developed an electrode array capable of recording simultaneous epicardial and endocardial monophasic action potentials (MAPs) on the heart in-vivo. Using this technique, we measured right atrial dual surface MAPs in nine anesthetized open chest pigs during local cooling of the atrial epicardium and intravenous infusions of adenosine. Cooling of the atrial epicardium generated a temperature gradient across the atrial wall and produced MAP duration (MAPd) lengthening on both surfaces. Intravenous infusion of adenosine caused MAPd shortening on both surfaces. Some sites exhibited differences in MAPd across epicardial and endocardial sites that persisted during both interventions. These findings suggest that atrial repolarization has three dimensional characteristics at least in some locations, perhaps due to the presence of pectinate musculature on the endocardial surface.